The most common and best understood specific learning disability is dyslexia, or specific reading disability, a disorder that affects the development of word-level reading, reading rate, spelling, and certain aspects of oral language, particularly phonological awareness and word retrieval, but with verbal reasoning and listening comprehension intact. Both the assessment and the treatment of dyslexia have interested researchers for over a century, not only in education, but also in the fields of psychology and neurology. This chapter reviews this disorder from three varying theoretical, scientific, and practical perspectives or models: cognitive-psychological, which emphasizes exploration of a learner's strengths and weaknesses in an attempt to understand the reasons for the reading failure; medical/neurobiological, which addresses the etiology, basis and mechanisms, explaining and predicting the symptoms; and educational, which is driven by legal mandates, as well as services provided by school systems. Each model offers insights into and contributes to the fullest understanding of the nature of this disability, as well as the conceptual and methodological frameworks that can contribute to the formulation of a diagnosis.